1. Field of the Invention
The present invention relates to a reinforcing structure for use with cardiovascular grafts. More particularly, the invention relates to the provision of a fibrous structure in the form of a coiled monofilament which is positioned within a biograft during formation of the biograft or which is coiled around an existing biograft and which becomes part of the biograft when collagen ingrowth takes place therearound.
2. Description of the Prior Art
Heretofore various graft structures which are reinforced against tearing have been proposed.
For example, the Ketharanathan U.S. Pat. No. 4,319,363 discloses a vascular graft or prosthesis which is reinforced with a mesh into which collagen ingrowth takes place.
Also, the Kaster U.S. Pat. No. 4,441,215 discloses a vascular graft made of synthetic material having a braided inner layer and compliant outer covering layer. The braided layer comprises a plurality of interwoven groups of filaments made of plastic or metal with the filaments being joined at the ends of the formed graft by tacking of adjoining filaments.
Further, as disclosed in the Mano et al. U.S. Reissue Pat. No. RE. 31,618, a polytetrafluoroethylene graft with reinforcing structure can be formed by winding a coil of elastic fibers therearound and then fixing the fibers around the graft by solvent bonding. Here, since the graft is completely made of synthetic materials, the reinforcing fibers are only positionable on the outside of the graft and cannot be incorporated within the graft structure itself. Fibers can be wrapped closely in contact with one another or at some interval, with the resiliency or radial compliance being determined by the elasticity of the fibers utilized and the solvent bonding thereof to the graft.
Due to the nature of the reinforcing structures proposed in the patents referred to above, grafts formed according to the teachings of those patents are limited with regard to radial compliance, i.e., the ability to increase the internal diameter of the graft. Such ability of increasing internal diameter is very important with regard to minimizing the possibility of thrombosis.
Also, such prior art grafts are limited by kinking. Knitted or woven meshes kink while a spring configuration does not kink.
The graft with reinforcing structure of the present invention provides for radial compliance of the graft structure by providing a loosely wound coil of monofilament either within the wall of the graft structure being formed or by placing the coil around the graft structure and allowing collagen ingrowth to secure the coil to the graft structure. The provision of a wound coil, with a predetermined pitch to the turns of the coil, provides a graft structure where the internal diameter of the structure can vary with flexing of the graft structure. Also, the smaller the angle of pitch, the greater the radial compliance.